Intake and/or exhaust gas sensors may be operated to provide indications of various exhaust gas constituents. Output from an oxygen sensor, for example, may be used to determine the air-fuel ratio (AFR) of exhaust gas. Similarly, an oxygen sensor may be disposed in an engine intake passage to determine the AFR of intake gas. In both cases, indications of intake and exhaust gas AFR may be used to adjust various engine operating parameters such as fueling and a target AFR, for example. In particular, exhaust gas AFR may be controlled to achieve the target AFR in order to maximize operating efficiency of an emission control device. For some oxygen sensors, their output may significantly vary as a function of their operating temperature. As such, these oxygen sensors may be heated by a heating element to achieve a desired operating temperature range such that desired oxygen sensing is provided.
The inventors herein have recognized that aging in an oxygen sensor such as a universal exhaust gas oxygen (UEGO) sensor can change the relation between temperature and impedance. For example, an impedance that results in a desired sensor temperature in a non-aged UEGO sensor may differ from an impedance that results in the desired sensor temperature in an aged UEGO. Without compensating this change in the relation between sensor temperature and impedance, the heater of the aged UEGO may be controlled to achieve the impedance that would achieve the desired sensor temperature in the non-aged UEGO sensor. Instead, an undesired sensor temperature which overshoots the desired sensor temperature may result, which may cause inaccurate sensor output and thus degraded engine operation.
U.S. Pat. No. 4,178,793 discloses an apparatus for measuring the impedance of an exhaust gas oxygen sensor. In one example, an oxygen sensor includes a variable internal impedance and is connected in series with a reference impedance and a semiconductor switch. A constant current source supplies current to a junction of the sensor and reference impedance at one sensor terminal to provide a minimum current and small switch impedance when the sensor impedance is large. The magnitude of the voltage at the one sensor terminal with the semiconductor switch in its conducting and non-conducting states may be sampled. The ratio of the magnitudes varies with sensor impedance. The ratio may be compared with one or more references to, in some examples, control operation of a sensor heater. In some scenarios, the comparison may prompt heating of the sensor via the heater to achieve a desired sensor impedance.
The inventors herein have recognized several issues with the approach identified above. While provision of dedicated sensor impedance sensing circuitry may facilitate sensor impedance measurement over time, inclusion of the circuitry increases the cost, complexity, and packaging space associated with the sensor arrangement. Moreover, other factors that can affect oxygen sensing are not accounted for—e.g., humidity. Inaccurate oxygen sensing may nevertheless result despite the ability to measure oxygen sensor impedance.
One approach that at least partially addresses the above issues includes a method of operating an oxygen sensor, comprising adjusting an impedance setpoint based on a change in dry air pumping current of the oxygen sensor
In a more specific example, a heating element coupled to the oxygen sensor is adjusted responsive to the adjusted impedance setpoint.
In a more particular example, the impedance setpoint is adjusted based on a desired operating temperature of the oxygen sensor.
In another aspect of the example, an operating temperature of the oxygen sensor is a function of the adjusted impedance setpoint.
In yet another aspect of the example, the oxygen sensor is a universal exhaust gas oxygen sensor.
In this way, changes in a relation between impedance setpoint of an oxygen sensor and a resulting operating temperature may be compensated. Thus, the technical result is achieved by these actions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.